spec: requires ceph base instead of common

spec: requires ceph base instead of common

Currently rbd-mirror and radosgw packages installation won't create the
Ceph directories in /var/lib/ceph since they depend on ceph-common
only. ceph-base is responsible for creating these directories.

Since ceph-base requires ceph-common then let's use ceph-base as a
dependency.

Fixes: http://tracker.ceph.com/issues/37620
Signed-off-by: Sébastien Han <seb@redhat.com>
(cherry picked from commit c0f77bd69ed0f0d813b1e9c2dd7375828fd42503)

Conflicts:
	ceph.spec.in : Resolved for ceph-base